If you plan to extend your license for 6 or 12 months, you should do so before the end of your current license.
After the license period ends, you have a grace period of 15 days to work without limitation. If you do not extend the license, then your Bitrix24 instance will be put on the free plan, with a 5 GB limit and functionality corresponding to the free plan.
If the amount of data in your Bitrix24 instance exceeds 5 GB, then after the grace period mentioned above, data will be accessible only for reading and deleting. You will not be able to load new files, tasks, input data into the CRM, or perform other actions until the data is below the 5 GB limit.
As soon as the amount of data is below 5GB, all the functionality of the free plan will be engaged, and use of the free version can continue indefinitely.
However, if no user authorises over the course of one month after the 15-day grace period, then the account 'freezes', and can be opened only by having an administrator (an employee of your company with administrator rights in your Bitrix24 instance) log in.
If no administrator logs in over the course of another 15 days after the account 'freezes', the Bitrix24 instance will be deleted.